1. Field of the Invention
The present invention relates to cable television transmission components. More particularly, the invention relates to an apparatus used in conjunction with a cable television tap. The apparatus allows servicing of the cable television tap without interruption of the cable signal to downstream subscribers and minimizes the chance of a short circuit in the system.
2. Description of Related Art
Cable television (CATV) services are provided to subscribers through transmission networks that include taps, splitters, amplifiers and other equipment that distribute CATV service and ensure that the CATV signal quality is maintained. In particular, taps reside along the network to provide access outlets for localized subscribers. CATV network and service as used herein refers to all systems involving the transmission of television signals from the headend over a transmission medium, such as fiber optic cable or coaxial cable.
FIG. 1 is a block diagram of a CATV network 5. The transmission line 34 provides cable signals from the headend 32 to subscribers 38, 39 at remote locations. The subscribers 38, 39 receive signals through taps 36, 37 placed along the transmission line 34. The CATV signals are typically routed into the tap and through a printed circuit board attached to the tap cover which splits the signal and allows each tap 36, 37 to typically provide a connection to four or more subscribers.
Referring to FIG. 2, a prior art CATV multiple tap 15 is shown. The multiple tap 15 generally includes a tap cover 10, a printed circuit board 14, a pair of terminal housings 40 and a main housing 26. The tap cover 10 is provided with a plurality of tap outlets 12, each of which provides CATV service to a different subscriber. The printed circuit board 14 is rigidly attached to the inside surface of the cover 10 and includes a pair of signal receptors 22, 23. The signal receptors 22, 23 allow the signal to flow through the printed circuit board 14 and to be split among the subscribers fed from the tap outlets 12. The signal also passes through the tap 15 to a downstream tap 37. A detailed explanation of the function of the printed circuit board 14, which is well known to those skilled in the art, is outside the scope of the present invention. A metal braid 11 surrounds the periphery of the printed circuit board 14 at the junction between the cover 10 and the main housing 26. The metal braid 11 provides an EMI/RFI trap for the printed circuit board 14.
The main housing 26 includes threaded signal ports 24, 25 at opposing ends. The input signal port 24 is adapted to receive a signal input via a coaxial cable and a signal impact connector 50. The output signal port 25 receives a signal output connector 51 for outputting the received signal to the downstream CATV network. The internal conductor 52, 53 of each coaxial cable 50, 51 is connected inside the tap 15 at a terminal housing 40. A threaded plug port 27 is provided adjacent to each signal port 24, 25 to allow plugs 28 to be removed. Exposed terminal screws 46 aligned with the ports 27 are tightened onto the conductors 52, 53 to fix each to a contact terminal 42 positioned in the respective terminal housing 40 (see FIG. 5). The components of the terminal housing 40 are shown in greater detail in FIG. 4. Upon engagement of the cover 10, the receptors 22, 23 on the printed circuit board 14 engage the contact terminals 42 to complete the circuit.
Referring to FIG. 3, the uninterrupted signal path 16 for the CATV tap 15 is illustrated. When the cover 10 is installed, the signal, shown as line 16, originates from the signal input connector 50. The signal input conductor 52 contacts the contact terminal 42 within the first terminal housing 40 and the signal flows through the contact terminal 42 to the first signal receptor 22 on the printed circuit board 14. The signal then flows through the printed circuit board 14 (and thus to each individual tap 12) and to the second signal receptor 23. The second signal receptor 23 is coupled to the second contact terminal 42 within the other terminal housing 40 which contacts the conductor 53 within signal output connector 51.
Periodically, the taps 36, 37 require servicing due to malfunctioning of the tap 36, 37 or to connect or disconnect subscribers 38, 39. However, when the cover 10 is removed for servicing the tap 15, the printed circuit board 14 is also removed and the signal path is open-circuited since the signal receptors 22, 23 no longer are connected to the contact terminals 42. As a result, removal of the cover results in interruption of the cable signal over the transmission line 34 to subscribers downstream from that tap. For example, returning to FIG. 1, servicing of the tap 36 not only results in interruption of service to the subscribers 38 who are fed from that tap 36, but also subscribers 39 who access the CATV network 5 through the downstream tap 37. Because of the increasing reliance upon the CATV system for lifesaving and other data critical applications, even a momentary signal interruption is undesirable. However, there is often no provision for maintaining uninterrupted service to downstream subscribers when the cover of the tap is removed for servicing.
One system for providing uninterrupted downstream service during servicing of a tap device is described in detail in U.S. Pat. No. 5,756,935 which issued May 26, 1998 and is commonly assigned with the present invention. This system provides an internal bypass switch 60, see FIG. 6, which maintains signal flow when the cover 10 is removed. The bypass switch 60 includes a flexible leaf spring bypass conductor 62. As shown in FIG. 6, removal of the tap cover 10 causes the conductor 62 to automatically contact both contact terminals 42 to thereby maintain uninterrupted service to downstream subscribers. When the tap cover 10 is replaced, see FIG. 7, an actuator 64 disengages and grounds the leaf spring bypass conductor 62 and the signal again flows through the printed circuit board 14.
One problem which occasionally occurs with this type of bypass switch 60 is a short circuit. With the tap cover 10 in place, both ends 63 of the bypass conductor 62 are grounded against the tap housing 26. As the tap cover 10 is removed, one of the ends 63 of the bypass conductor 62 may move into contact with its respective contact terminal 42 while the other end 63 is still grounded against the tap housing 26. This will generally result in a short circuit. Since it may be difficult for a service technician to tell if a tap 15 which is about to be serviced includes a bypass switch 60, it is prudent to treat each tap 15 as if it has a bypass switch 60 with the potential for a short circuit.
Accordingly, it is an object of the invention to provide a bypass system which minimizes the chance of a short circuit while maintaining uninterrupted service to downstream subscribers during removal of the tap cover for servicing.